I usually record the engine, motor sound of the train as a hobby.

Recently, I bought a new ZOOM F3 recorder and Clippy EM272Z1 microphone and recorded it, but sometimes in the underground section, the input level is lowered (to the point of being close to silence) and then comes back to normal. (To be honest, it happens quite often, once every minute or two.)

I don't know if it's due to RF interference or if the limiter is operating in F3, but it happens under certain conditions or randomly depending on the type of train.

I would appreciate it if you could let me know if you have any stories to help me solve this problem.

Could changing the microphone be the solution?

The budget is about 250 dollars. and I'd like to do a stereo recording.

  • Behringer C-2
  • ZOOM ZPC-1 I'm thinking between the two above, which one would be good? You can also recommend other microphones.

*I used a translator. Please understand my poor English skills.

Add details below.

Basic information

miking method: ORTF Channel: Stereo Used Material: Clippy EM272Z1 + ZOOM F3 Recording format: 48k 32-bit float

- Major Problem Situation When recording a drive in a tunnel, the input level is randomly lowered and then returned. (It occurs in the underground section of all routes regardless of the route)

- a condition that usually occurs (IGBT Vehicle) Opening/Closing the Door (PMSM vehicles) At acceleration and deceleration

- Why RF interference is suspected

  1. As the problem develops, occasional RF noise comes in.
  2. It does not occur in the ground section, but only in the tunnel section.

- Other than that

  1. It is too early to dismiss it as a matter of RF interference, given that it only occurs when the door is opened and closed, as in the case of an IGBT vehicle.
  2. However, in the case of PMSM vehicles, noise is often mixed at the same time as the phenomenon occurs, so it is difficult to rule out the influence of RF interference.
  3. Judging from the cases of 1 and 2, it may be a phenomenon caused by a combination of effects.

*I have uploaded the recording file and time table that caused the problem to Google Drive.


  • Is there a limiter in the Zoom F3? If so have you tried turning it off? Aug 26 at 17:23
  • It is not clear whether a limiter exists in ZOOM F3. It's just a guess that came up because the problem situation is similar to the sound that occurs when the limiter is working. Unfortunately, F3 doesn't seem to have a separate limiter setting or a way to turn it off. :( Aug 27 at 3:19
  • What are you seeing or hearing that leads you to say the input level is changing? It might be the microphone. According to the Zoom F3 manual: "The F3 records in 32-bit float format, so the input gain does not need to be adjusted." I don't think there is a limiter or even input gain control on the F3 because it is always recording in a floating point audio format. That means the decimal point for each sample value is moved to scale the sample appropriately and there is no full scale sample level that would cause clipping. I'm a little skeptical about RF being related. Aug 27 at 4:39
  • Can you give a time stamp in the file where we can hear the problem? Oh I think I hear it. Right when the doors open there's a brief dropout? Is there a burst of wind when the doors open? If so, that could be hitting the mic and causing the problem. Could be the mic is overloading for some reason when the doors open. Aug 27 at 4:39
  • Maybe there's a powerful RF burst created by the door electronics when they open? Seems like a strange thing to me. If that is the problem, then I'm pretty sure it's the mic that is affected, and not the recorder itself. The mic cable would act like an antenna. Also it looks like an electret condenser mic, so a powerful enough EM field could cause the plates to have a problem. Aug 27 at 4:46


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.